Expand "Geometry" when Dynamo starts

#### Purpose

Make `Category` as expanded when Dynamo starts.

#### Modifications

Added function call to `DynamoModel.PostUIActivation` to expand `Geometry` call.

#### Unit Test

![image](https://cloud.githubusercontent.com/assets/8158551/5086417/e72a7590-6f24-11e4-8351-660106706a86.png)

#### Additional references

[MAGN-5455](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-5455).

#### Reviewers

@Benglin, please, take a look.